
#1
Mar2713, 04:10 AM

P: 43

Hi, in my book there are two capacitor plates distance x apart (they are kept connected to a constant voltage source). These plates are moved apart to distance 3x. In order to find the work done to move the capacitors apart (using W=F dl=QE dl), my book takes the charge Q of one plate and electric field felt on that one plate and integrates it from x to 3x. Why can't we take the take the charge and electric field felt on both plates and integrate half the distance of x to 3x?




#2
Mar2713, 04:51 AM

Mentor
P: 40,907





#3
Mar2713, 02:24 PM

P: 43





#4
Mar2713, 02:55 PM

Mentor
P: 40,907

Work to Move parallel capacitor PlatesCompare that to just moving one plate (like in your book). In that case y would be the total distance, so L = y. And you'd integrate from y = x to y = 3x. (And not multiply by 2.) Each method should give the same answer for the work done. 



#5
Mar2713, 03:14 PM

P: 43





#6
Mar2713, 03:36 PM

Mentor
P: 40,907





#7
Mar2713, 04:07 PM

P: 43





#8
Mar2713, 04:19 PM

Mentor
P: 40,907





#9
Mar2713, 04:32 PM

P: 43





#10
Mar2713, 05:39 PM

Mentor
P: 40,907

But since the two plates experience the same force and movement, why not take advantage of symmetry? 



#11
Mar2713, 06:03 PM

P: 43

Thanks!



Register to reply 
Related Discussions  
parallel plate capacitor by an electric field between the plates  Introductory Physics Homework  1  
Parallel Plate Capacitor  Finding E field between plates  Introductory Physics Homework  13  
Work required to move capacitor plates  Introductory Physics Homework  7  
Force between parallel plates in a capacitor  Introductory Physics Homework  1  
work to move two plates  Introductory Physics Homework  13 